Backside Illumination (BSI) image sensor chips are replacing front-side illumination sensor chips for their higher efficiency in capturing photons. In the formation of the BSI image sensor chips, image sensors and logic circuits are formed on a silicon substrate of a wafer, followed by the formation of an interconnect structure on a front side of the silicon substrate. The interconnect structure includes a plurality of metal layers including bottom metal layer M1 through top metal layer Mtop. A passivation layer is then formed over the interconnect structure.
The formation of the image sensor chips involves a backside grinding, a p-type impurity implantation, and an anneal. The process is then continued to form backside contact pads, color filters, lenses, and the like, on the backside of the silicon substrate.